In treating diseased vessels, particularly blood vessels which have one or more side branches extending from a main vessel, difficulties may arise when implanting stents at these junctions to treat lesions. For instance, when implanting a stent along the main vessel, the openings to the side branches may become restricted by the stent walls. Although open cells along the stents may be expanded in size to allow for greater flow between the main vessel and side branch, such enlarging of the open cells may present additional challenges.
For instance, enlarging the open cell may create a number of cracks or failures in the stent struts. This may be the case particularly when attempting to enlarge an open cell in a bioresorbable polymeric stent or scaffold.
Because many polymeric implants such as stents are fabricated through processes such as extrusion or injection molding, such methods typically begin the process by starting with an inherently weak and brittle material. In the example of a polymeric stent, the resulting stent may be susceptible to brittle fracture especially upon expansion. Also, as described above, due to their inherent weakness and embrittlement, a selective enlargement of the cell is not possible with these stents without causing mechanical failure in their structure.
A stent which is susceptible to brittle fracture is generally undesirable because of its limited ability to collapse for intravascular delivery as well as its limited ability to expand for placement or positioning within a vessel. Moreover, such polymeric stents also exhibit a reduced level of strength. Brittle fracture is particularly problematic in stents as placement of a stent onto a delivery balloon or within a delivery sheath imparts a substantial amount of compressive force in the material comprising the stent. A stent made of a brittle material may crack or have a very limited ability to collapse or expand without failure. Thus, a certain degree of malleability is desirable for a stent to expand, deform, and maintain its position securely within the vessel.
Accordingly, it is desirable to produce a polymeric substrate having one or more layers which retains its mechanical strength and is sufficiently ductile so as to prevent or inhibit brittle fracture, particularly when utilized as a biocompatible and/or bioabsorbable polymeric stent for implantation within a patient body. Additionally, it is desirable to produce a polymeric stent which can be deployed and expanded within a vessel lumen and then have one or more open cells defined along the stent further enlarged without cracking or failure of the struts.